In order to prevent that a luminescent spot or a high contrast image formed in an observation field, in particular, in a frame is reflected from a surface of a protection window provided on the last optical surface for dustproof and the like, focused again in the vicinity of a focal plane of the eyepiece, and observed as a ghost image, there has been an eyepiece optical system in which an antireflection coating and the like is applied on the surface of the protection window. However, in such an eyepiece optical system, it has been difficult to suppress ghost images when the contrast of the real image is extremely strong.
Accordingly, in order to prevent ghost images in the field of view when the contrast is extremely strong, a finder optical system in which a protection window member has curvature has been proposed (see, for example, Patent Document 1).